Warnings of flooding Friday in the Australian state of Victoria tell the story of slow-moving downpours. Thunderstorms have a habit of dropping vast amounts of water in no time. That is why some cities have permanent storm drains.

Most places don’t have that provision so flash flooding is a risk in storm season which washes away farmland and roads. The state of Victoria is not unique in having a current flood risk.

There is a near stationary regenerating line of thunderstorms reaching from Victoria, through South Australia and the Macdonnell Ranges of Northern Territory to the Kimberley Plateau in Western Australia.

For South Australia, senior meteorologist Brett Gage said that towns such as Oodnadatta and Marree, were expected to receive up to 15 times their monthly average rainfall during the next few days.

The Bureau of Meteorology said the heaviest falls of up to 200 millimetres are expected in the far north of the state, but the Flinders Ranges will also be one of the worst hit areas.

This could end up being the worst flood event for decades as a lot of tropical air is being brought into this wide ribbon of thunderstorms. The Australian Bureau of Meteorology states that this rare weather pattern, not seen in South Australia for over 40 years, is behind the heavy rainfall forecast.